Seyed Alireza Hassani

Cholinergic, dopaminergic and serotonergic neuromodulation has pervasive effects on circuit functions in prefrontal cortex (PFC) and striatum and interact with glutamatergic and GABAergic transmission. But how these neurochemicals interact during cognitive engagement is largely unknown and inferred from studying few neuromodulators at a time. Here, we sampled the extracellular availabilities of five neurochemicals in the PFC and striatum of nonhuman primates and tested how they changed when subjects switched from rest to engage in a cognitive set shifting task using miniaturized probes for diffusion-based solid-phase microextraction. Cognitive engagement was best predicted by GABAergic and cholinergic changes in the PFC, and dopaminergic and cholinergic changes in the striatum. Glutamate co-modulated with acetylcholine across states in both the PFC and striatum, while serotonin changes in PFC and striatum correlated consistent with common external modulation. These findings document an area-specific multi-neuromodulatory fingerprint of an adaptive cognitive state in the fronto-striatal network of the nonhuman primate brain.

The noradrenergic system is implicated to support behavioral flexibility by increasing exploration during periods of uncertainty and by enhancing working memory for goal-relevant stimuli. Possible sources mediating these pro-cognitive effects are α2A adrenoceptors (α2AR) in prefrontal cortex or the anterior cingulate cortex facilitating fronto-striatal learning processes. We tested this hypothesis by selectively stimulating α2ARs using Guanfacine during feature-based attentional set shifting in nonhuman primates. We found that α2A stimulation improved learning from errors and facilitates updating the target feature of an attentional set. Neural recordings in the anterior cingulate cortex (ACC), the dorsolateral prefrontal cortex (dlPFC), and the striatum showed that α2A stimulation selectively enhanced the neural representation of negative reward prediction errors in neurons of the ACC and of positive prediction errors in the striatum, but not in dlPFC. This modulation was accompanied by enhanced encoding of the feature and location of the attended target across the fronto-striatal network. Enhanced learning was paralleled by enhanced encoding of outcomes in putative fast-spiking interneurons in the ACC, dlPFC, and striatum but not in broad spiking cells, pointing to an interneuron mediated mechanism of α2AR action. These results illustrate that α2A receptors causally support the noradrenergic enhancement of updating attention sets through an enhancement of prediction error signaling in the ACC and the striatum.

Acetylcholine (ACh) in cortical neural circuits mediates how selective attention is sustained in the presence of distractors and how flexible cognition adjusts to changing task demands. The cognitive domains of attention and cognitive flexibility might be differentially supported by the M ₁ muscarinic cholinergic sub-receptor. Understanding how M ₁ mechanisms support these cognitive subdomains is of highest importance for advancing novel drug treatments for conditions with altered attention and reduced cognitive control including Alzheimer’s disease or schizophrenia. Here, we tested this question by assessing how the subtype selective M ₁ -receptor specific positive allosteric modulator (M ₁ PAM VU0453595) affects visual search and flexible reward-learning in nonhuman primates. We found that allosteric potentiation of the M ₁ receptor enhanced flexible learning performance by improving extra-dimensional set shifting, by reducing latent inhibition of previously experienced distractors, and by reducing response perseveration in the absence of adverse side effects. These pro-cognitive effects occurred in the absence of apparent changes of attentional performance during visual search. In contrast, non-selective ACh modulation using the acetylcholinesterase inhibitor donepezil improved attention during visual search at doses that did not alter cognitive flexibility and that already triggered gastrointestinal cholinergic side effects. These findings illustrate that M ₁ positive allosteric modulation enhances cognitive flexibility without affecting attentional filtering of distraction, consistent with M ₁ activity boosting the effective salience of relevant over irrelevant objects. These results suggest that M ₁ PAMs are versatile compounds for enhancing cognitive flexibility in disorders spanning schizophrenia and Alzheimer’s diseases. Statement of significance: Muscarinic receptors mediate the pro-cognitive effects of acetylcholine, but it has remained unclear whether they differentially affect the cognitive subfunctions of attentional filtering, set shifting, and learning. To clarify the functional specificity of M ₁ receptors, we assessed these diverse functions using a recently developed, highly selective M ₁ PAM. This M ₁ PAM caused domain-specific cognitive improvement of flexible learning and extra-dimensional set shifting, reduced perseverations and enhanced target recognition during learning without altering attentional filtering functions. These domain-specific improvement contrasted to effects of a non-selective acetylcholinesterase inhibitor that primarily enhanced attention and caused dose limiting adverse side effects. These results demonstrate domain-specific improvements of cognitive flexibility suggesting M ₁ PAMs are versatile compounds for treating cognitive deficits in schizophrenia and Alzheimer’s disease.

Nonhuman primates (NHP’s) are self-motivated to perform cognitive tasks on touchscreens in their animal housing setting. To leverage this ability, fully integrated hardware and software solutions are needed that work within housing and husbandry routines while also spanning cognitive task constructs of the Research Domain Criteria (RDoC). Here, we detail such an integrated robust hardware and software solution for running cognitive tasks in cage-housed NHP’s with a cage-mounted Kiosk Station (KS-1). KS-1 consists of a frame for mounting flexibly on housing cages, a touchscreen animal interface with mounts for receptables, reward pumps, and cameras, and a compact computer cabinet with an interface for controlling behavior. Behavioral control is achieved with a Unity3D program that is virtual-reality capable, allowing semi-naturalistic visual tasks to assess multiple cognitive domains.KS-1 is fully integrated into the regular housing routines of monkeys. A single person can operate multiple KS-1’s. Monkeys engage with KS-1 at high motivation and cognitive performance levels at high intra-individual consistency. KS-1 is optimized for flexible mounting onto standard apartment cage systems and provides a new design variation complementing existing cage-mounted touchscreen systems. KS-1 has a robust animal interface with options for gaze/reach monitoring. It has an integrated user interface for controlling multiple cognitive tasks using a common naturalistic object space designed to enhance task engagement. All custom KS-1 components are open-sourced.In summary, KS-1 is a versatile new tool for cognitive profiling and cognitive enrichment of cage-housed monkeys. It reliably measures multiple cognitive domains which promises to advance our understanding of animal cognition, inter-individual differences, and underlying neurobiology in refined, ethologically meaningful behavioral foraging contexts.

BACKGROUND Donepezil exerts pro-cognitive effects by non-selectively enhancing acetylcholine (ACh) across multiple brain systems. The brain systems that mediate pro-cognitive effects of attentional control and cognitive flexibility are the prefrontal cortex and the anterior striatum which have different pharmacokinetic sensitivities to ACh modulation. We speculated that these area-specific ACh profiles lead to distinct optimal dose-ranges for donepezil to enhance the cognitive domains of attention and flexible learning. METHODS To test for dose-specific effects of donepezil on different cognitive domains we devised a multi-task paradigm for nonhuman primates (NHPs) that assessed attention and cognitive flexibility. NHPs received either vehicle or variable doses of donepezil prior to task performance. We measured donepezil intracerebral and how strong it prevented the breakdown of ACh within prefrontal cortex and anterior striatum using solid-phase-microextraction neurochemistry. RESULTS The highest administered donepezil dose improved attention and made subjects more robust against distractor interference, but it did not improve flexible learning. In contrast, only a lower dose range of donepezil improved flexible learning and reduced perseveration, but without distractor-dependent attentional improvement. Neurochemical measurements confirmed a dose-dependent increase of extracellular donepezil and decreases in choline within the prefrontal cortex and the striatum. CONCLUSIONS The donepezil dose for maximally improving attention functions differed from the dose range that enhanced cognitive flexibility despite the availability of the drug in the major brain systems supporting these cognitive functions. Thus, the non-selective acetylcholine esterase inhibitor donepezil inherently trades improvement in the attention domain for improvement in the cognitive flexibility domain at a given dose range.